drm/msm/a6xx: Remove both GBIF and RBBM GBIF halt on hw init

Currently we're only deasserting REG_A6XX_RBBM_GBIF_HALT, but we also
need REG_A6XX_GBIF_HALT to be set to 0.

This is typically done automatically on successful GX collapse, but in
case that fails, we should take care of it.

Also, add a memory barrier to ensure it's gone through before jumping
to further initialization.
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/542760/Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a6xx_gpu.c

@@ -1111,8 +1111,12 @@ static int hw_init(struct msm_gpu *gpu)
 	a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_GPU_SET);
 
 	/* Clear GBIF halt in case GX domain was not collapsed */
-	if (a6xx_has_gbif(adreno_gpu))
+	if (a6xx_has_gbif(adreno_gpu)) {
+		gpu_write(gpu, REG_A6XX_GBIF_HALT, 0);
 		gpu_write(gpu, REG_A6XX_RBBM_GBIF_HALT, 0);
+		/* Let's make extra sure that the GPU can access the memory.. */
+		mb();
+	}
 
 	gpu_write(gpu, REG_A6XX_RBBM_SECVID_TSB_CNTL, 0);